1. Field of the Invention
The present invention relates to disposable blow-molded pressure-resistant plastic bottles having particular utility as containers for carbonated beverages. The present invention relates particularly to such a plastic bottle having a bottom design employing a continuous seating ring upon which the bottle rests when placed on a smooth horizontal surface in a normal upright position. The present invention further relates to a novel bottom design within the seating ring which will not evert when the bottle is sealed and the inside of the bottle subject to substantial pressure due to containment of a carbonated beverage or the like.
2. Summary of the Prior Art
Blow-molded plastic bottles for containing liquids at elevated pressures are known and have found increasing acceptance particularly in the beverage industry for use as one-way disposable containers. Plastic bottles of this type are subject to a number of structural and functional criteria which have presented many problems not previously considered. Solutions to the problems offered by the prior art have yielded interesting results but have not been entirely satisfactory.
Some of the criteria which must be considered are the flexible properties of the plastic making up the bottle particularly where the contained liquid will be carbonated and thus present an elevated pressure within the bottle when sealed which will be absent both prior to sealing and subsequent to opening the bottle. Moreover, the bottle must conform to the size and shape of prior art glass bottles employed for the same purpose so as to conform to the handling requirements of the existing equipment used in filling the bottles. Further, the plastic bottle, blown from a parison, is limited to certain modification by the very nature of the blowing process and the available materials for use in forming such a bottle.
When used with carbonated beverages, the bottle may be subjected to internal pressures normally between 40 and 100 psi and occasionally as high as 200 psi under severe conditions. The load experienced by the plastic bottle is greatest at the bottom of the container. Various designs have been employed to effectively deal with this load condition, the designs falling into three general subclasses.
The first sub-class of bottom design is typified by U.S. Pat. No. 3,722,725 and consists generally of a hemispherical bottom to which is added, as a separate member, a base cup which supports the bottle in an upright position. While this basic design has been widely adopted, the required assembly of the two pieces to form the self-supporting bottle is an undesirable feature requiring assembly time, manpower and machinery which might be eliminated if a satisfactory one-piece bottle could be designed.
The second sub-class of bottom designs is typified by U.S. Pat. No. 3,759,410 wherein a plurality of feet are integrally formed in the base of the bottle upon which the bottle rests. While this design has the advantage of the single element construction, the nature of the blowing process and the resins employed make reliable formation of the feet difficult often resulting in uneven stresses which may cause a "rocker effect" of the bottle when sealed. There has also been some resistance to the acceptance of this type of bottle design due in part to its "different" look.
The third sub-class of bottom designs, and the sub-classes in which the present invention resides, is represented by U.S. Pat. Nos. 3,468,443; 3,511,401; 3,643,829; 3,722,726; and 3,870,181. The bottom of each of these designs includes a continuous peripheral seating ring upon which the bottle rests surrounding a concave central portion. This concave central portion forms a space which is not included within the bottle itself, but rather is between the bottle bottom and any planar surface upon which the bottle is placed. The term "excluded volume" is adopted to conveniently refer to this space. Various designs have been adopted for that portion of the bottle bottom within this seating ring which are intended to strengthen the bottle bottom and prevent the bottom from everting when subjected to internal pressure. Particular constraints are presented when the resins employed achieve maximum strength upon bi-axially stretching. Further none of the prior art designs of this sub-class have provided for "parison tip capture" relative to blowing mold prior to the blowing process.
It is therefore an aim of the present invention to provide a design for a blow-molded one piece plastic beverage container having a continuous seating ring with bottom design which will not evert under pressure yet will provide for centering of the parison within the blowing mold thereby assuring axial uniformity in the structure of a bottle employable on presently existing conventional bottling equipment.